This invention relates to throttle valve means arranged in the hydraulic circuit of an automatic transmission and, more particularly, to a throttle valve assembly for displacing the pressure regulating means of at least two throttle valves in correspondence with the degree of throttle opening of an engine.
The growing popularity of vehicles having an automatic transmission has been accompanied by stricter evaluation of the speed change performance of such transmissions. In particular, a speed-change shock produced when a gear train is changed over to alter the speed-change ratio can only be evaluated in terms of "feel", and even a slight shock of this kind is annoying. Various methods and apparatus have heretofore been proposed and put into practical use in order to mitigate or eliminate such speed-change shock. Furthermore, coupled with the trend toward front-engine automotive vehicles with front wheel drive, there is a demand for automatic transmissions which are smaller and lighter in weight.
Fundamental in smoothly controlling the speed change of an automatic transmission is to adopt a method of varying main pressure, mainly the pressure of the fluid which actuates the frictional engaging means that administers speed change control in dependence upon the output of the engine. Ordinarily, main pressure is varied by a throttle valve assembly which generates pressure (throttle pressure) commensurate with the throttle opening of the engine. The throttle pressure, in cooperation with governor pressure dependent upon vehicle speed, is also used as a signal which changes over shift control valves.
A throttle valve assembly of this type is disclosed in the specification of Japanese Utility Model Application Laid-Open No. 58-135547. The disclosed throttle valve assembly is adapted to apply a throttle pressure, which is produced by a second throttle valve, as back pressure of an accumulator for controlling the extent to which pressured oil is supplied to frictional engaging means, and to changeover the shift control valve by employing throttle pressure, which is produced by a first throttle valve, in cooperation with governor pressure. As for the pressure regulation of the first and second throttle valves, plungers inside the valves are displaced by levers connected to the accelerator pedal, and a load acting upon a pressure regulating spring is changed by the plungers.
Alternatively, rotary cams may be used in place of the levers, in which case the cams are made to rotate by cables connected to the engine throttle.